1. Field of the Invention
The present disclosure relates generally to a semiconductor released beam device, and in particular but not exclusively, relates to a semiconductor released beam device fabricated in trenches.
2. Description of the Related Art
Micro-electromechanical systems (MEMS) in semiconductors have arisen for various applications to sense temperature, pressure, strain, acceleration, rotation, chemical properties of liquids and gases, etc. Those MEMS structures are usually combined with other integrated circuits, such as metal oxide semiconductor (MOS) circuits or complimentary metal oxide semiconductor (CMOS) circuits, for analyzing and calculating the parameters sensed by MEMS. Therefore, the MEMS manufacturing processes are required to be compatible with the existing MOS or CMOS manufacturing processes such that the whole system is inexpensive, reliable, and compact.
Different MEMS structures in semiconductors have been proposed and developed for such various sensing purposes. For example, a released beam sensor was proposed in U.S. Pat. No. 5,917,226 for detecting temperature variation and an integrated released beam oscillator was proposed in U.S. Pat. No. 6,278,337. A similar released beam sensor was also proposed in U.S. Pat. No. 6,218,209 ('209 patent) for detecting acceleration and could be applied in airbag, anti-lock braking, or ride suspension systems for automobiles or in-flight aircraft monitoring systems.
The process sequence shown in the '209 patent includes the step of forming a sacrificial layer of material such as silicon dioxide above and in contact with a layer of material that serves as both an etch stop layer and a fixed contact layer, as shown in FIG. 1 of '209 patent. The layer of material that the released beam in formed from is located above and in contact with the sacrificial layer. The removal of the sacrificial layer in selected regions after the released beam material is patterned produced the structures that are used in sensor applications.
However, the released beam structure proposed in '209 patent could only detect the acceleration force in only one direction which is perpendicular to the surface of the substrate. Furthermore, even there is an etch stop layer under the sacrificial layer, there is no etch stop layer around the sides of the sacrificial layer and therefore it is difficult to control the etch process in the lateral direction when there are several released beam structures manufactured at the same time.